The present invention relates to a method for producing photographic pictures for the photogrammetric surveying of spatial objects of suitable pictures, wherein the spatial objects control points are established and two photographic shots, using central projection with different position of the projection center are produced. Then a method for evaluating the pictures taken in the photogrammetrical surveying of spatial objects is described, and a device is illustrated which is used in the manufacture of the photographic pictures.
The use of miniature pictures for terrestrial surveying is already known in the art. In the terrain, various control points are placed which must be surveyed before making the miniature picture. The control points must be placed in the terrain so as to surround the region to be photographed, so that later an interpolation is possible. To evaluate the pictures, the internal and external orientation must be determined. This means that for each camera, the calibrated focal length, c, which only approximates the focal length, the principal point and the distortion, and as external orientation the position of the projection center in space and the orientation of the photograph perpendicular according to the three solid angles must be determined and calculated. By means of the internal and external orientation, the coordinates of the object points can be determined from the coordinates of the image points on both photographs. This method is not suitable for evaluating traffic accidents, because the introduction of the individual control points and the subsequent geodetic surveying requires a relatively long period of time which is not available with accidents because the area as a rule must be cleared quickly. From the German Laid Open Document No. 2 430 851, coordinate measurement by means of photogrammetric methods is already known. Electronic TV camera tubes are used and a control point system, not described here, is introduced into the object area. With this method also, the dates of internal and external orientation must be determined. Also, with this method only discrete points (previously marked in the terrain) can be traced or their spatial position determined. With this method, the high information content of a photograph is absent. This method also is not suited for evaluating traffic accidents, because only the discrete points are present and an immovable evaluation of the accident is assumed, aside from the amount of time spent.
A photographic picture results from a central projective display of the object area on a plane (image plane). If the object is a plane, the image is unique i.e., an image point corresponds to an object point. Between these planes there is a colinear relationship which is completely described by the association of four corresponding points in both planes. A necessary requirement is that no three of the four points may lie on a straight line. If four such corresponding points in both planes are known, the position of any object points can be derived from associate image points; a single-picture measurement is sufficient.
However, to reconstruct a spatial (solid) body, a spatial object, from plane pictures, two pictures with spatially different positions of the projection centers (picture base b) must be taken and evaluated. If the geometrical parameters of the pictures are known, the picture optical path can be reconstructed and the object can be represented by the spatial intersection of hologue beams. This involves a two-picture measurement.
One of the general case of two-picture measurement, where the mutual position of the two shooting bundles of rays is arbitrary, the stereophotogrammetry forms a special case. Here the conditions are fulfilled which are related to the spatial perception of men. The shooting direction in this case should be parallel or convergent.
A photographic picture is considered as a photogrammetric picture when the geometric parameters of the image are known. These are the parameters of "internal orientation" namely
(a) the position of principal point H' in the image plane E, i.e., the orthogonal projection of the projection center O on the image plane E,
(b) the calibrated focal length c, i.e., the distance OH' and
(c) the distortion, i.e., the deviation from the central projection, due to the optical system.
The position of principal point H' in the image plane E is determined by the position coordinates x.sup.+, y.sup.+ in a cartesian image coordinate system (x.sup.+, y.sup.+). Marks on the picture frame whichare placed with each shot, define this local coordinate system.
A camera built up in this form is called a mapping camera. FIG. 1 shows the typical construction of such a mapping camera. The definition of the shooting geometry permits both the complete reconstruction of the shooting bundle of rays from the photographic image. The position of a shooting bundle of rays in space is established by the parameters of "external orientation" in its relation to a higher space coordinate system (reference system) x, y, z.
The six elements of "external orientation" are:
X.sub.o, Y.sub.o, Z.sub.o : space coordinates of projection center O in the reference system
. . : orientation angles to determine the shooting direction OH' in space and the orientation of image coordinate system x.sup.+, y.sup.+
Points in space where position in the reference system is known, are called control points.
Previously used methods are based on single-photograph measurement or two-photograph measurement.
In all cases, where one may assume that both image and object are a plane, a single-photograph measurement can be made. In the rectification of aerial photographs of flat terrain, this method is used in practice. When taking accident pictures the street surface is a plane, at least by stretches, and skidmarks on the road can be reconstructed from the pictures when the position of four points on the road can be determined and identified on the picture. For the calculative rectification, the following formulas for the central projective photographing (colinear relationship) hold: EQU X=(a.sub.1 x.sup.+ +a.sub.2 y.sup.+ +a.sub.3)/(c.sub.1 x.sup.+ +c.sub.2 y.sup.+ +1) EQU Y=(b.sub.1 x.sup.+ +b.sub.2 y.sup.+ +b.sub.3)/(c.sub.1 x.sup.+ +c.sub.2 y.sup.+ +1) (1)
where:
x.sup.+, y.sup.+ are the image coordinates
X, Y the object coordinates in the terrain
a.sub.1 . . . b.sub.2 . . . c.sub.2 the eight unknowns.
A total of eight unknowns must be determined. This condition is met by four points. The advantage of the method is, that, neglecting the distortion, no mapping cameras are required since the parameters of the internal orientation of the shooting camera need not be known.
In the two-image picture measurement, one uses stereo pictures since the evaluation of these pictures, the stereoscopic visual ability of man is used for the association of corresponding points in both pictures. Particularly in the terrestrial photogrammetry, as used for shooting traffic accidents, double mapping cameras, e.g., the stereo mapping camera SMK 120 of Zeiss with a fixed shooting base of +120 cm and glass plates as picture carriers are used.
A double mapping camera is made up of two mapping cameras. They are mounted on a common carrier with a known shooting base, making sure that the image planes and the image coordinate systems are parallel to each other. The external orientation is determined in relation to the perpendicular by having the double camera horizontal during a shooting. The advantage of this system is the establishment of inside and mutual orientation of the cameras and the possibility of a common external orientation. The disadvantage is high technical effort and resulting high cost for the cameras and the complicated handling.
Accordingly, it is an object of the present invention to avoid the disadvantages of the state of the art and to provide a method of the above type which permits the shooting of spatial objects with simple cameras, without using mapping cameras, with the pictures suitable for the photogrammetric survey with sufficient accuracy.
Another object of the present invention is to provide an arrangement of the foregoing character which may be simply carried out in a reliable manner.
A further object of the present invention is to provide an arrangement, as described, which may be readily maintained in service and which may be economically fabricated.